Affinity membranes are becoming widely accepted for use in immuno-affinity binding tests such as the Western Blot and Souther Blot techniques. This is the type of assay currently used for AIDS, Hepatitis B, and other virulent blood disease testing. Details of the technology of affinity binding have been summarized in a paper entitled "AFFINITY BINDING An Evolving Technology" presented at the 1984 Fourth Annual Membrane Technology/Planning Conference by Randall H. Morse.
Known polymer membranes possess mechanical strength and chemical resistance but lack hydrophilicity and passivity to proteins. Thus, the membrane is quickly fouled by adsorption of proteins or other biological materials. Methods for the modification of the membranes have involved chemical modification of the polysulfone aromatic ring by sulfonation, chloromethylation, nitration and Friedel-Crafts reaction; grafting a hydrophilic material onto a pre-formed film support; plasma polymerization of nitrogen-containing compounds directly onto porous polysulfone and blending of a hydrophilic, compatible additive such as polyvinylpyrrolidone with the polysulfone.
More specifically, the blending of polymers is known for altering the hydrophilic-hydrophobic balance of a membrane system. Inasmuch as most polymers are thermodynamically incompatible, polymer blending has heretofore found limited utility. The choices of appropriate polymers for the formation of compatible blends are limited to species where significant interaction can occur. Several recent patents have provided semipermeable membranes, ultrafiltration membranes and the like and processes for their preparation which involve mixing or blending of polymers.
U.S. Pat. No. 4,046,843 provides a process for preparing semipermeable membranes from one of several mixtures. One is a water-insoluble high polymer (polysulfone) and a water-soluble high polymer (polyethylene oxide). Another is a water insoluble high polymer (polysulfone) and a water soluble surfactant including anionic (sodium laurylsulfate), nonionic (polyoxyethylene lauryl ether) and natural surfactants (saponin). The membrane is formed by casting a solution of a foregoing mixture, exposing the formed article to a plasma for crosslinking and then washing the exposed article with water for removal of uncrosslinked water-soluble polymer or water-soluble surfactant.
U.S. Pat. No. 4,377,481 is directed toward blended polymeric membranes which comprise a water-insoluble matrix polymer and a water-insoluble copolymer. The latter comprises an acrylate or methacrylate monomer, the homopolymer of which is water-insoluble and matrix compatible while the second monomer contains cationic or anionic groups and which if homopolymerized would be water-soluble but matrix incompatible.
Despite the widespread existence of different processes for the extraction of proteins from fluids; the known filtration membranes and related processes and, the various techniques for modifying polymer membranes, the art has not recognized heretofore a process for the preparation of affinity membranes involving the modification of polymer blends to impart selective protein binding. As a result of the present invention non-fouling, affinity membranes have been obtained.